Lock zoom level

[demiantres]

Locus Maps has a useful feature for locking the zoom level. When locked then only raster tiles from a specific zoom level are used independent from the current map zoom level.

One option for the same effect in VTM is to implement a custom "UrlTileDataSource.query" (or "BitmapTileLoader.loadTile") method which stitches together a tile from multiple tiles or cuts out a region from an existing tile. But this is quite slow/complex.

Is there a better solution for a lock function?

[devemux86]

Displaying bitmap tiles from higher zoom levels would result in a blurry map.

All TileSource builders have methods to limit the zoom levels (see DefaultSources).
Could use a OverzoomTileDataSource like in vector maps (see MapilionMvtTileSource)?

[demiantres]

I have already tested an OverzoomTileDataSource but this won't work because it loads the wrong tiles. The problem here is that the tile image from the server does not actually match the tile to be shown in the map.

[devemux86]

So far it is being used without any problems in vector tile sources, like MapilionMvtTileSource.

[demiantres]

The attached video shows what happens when setting the overzoom to 14. Starting with zoom level 14 the tiles get messed up.

Untitled.video.mp4

Code:

// BitmapTileSource.java
// original:
new UrlTileDataSource(this, new TileDecoder(), getHttpEngine());

// modified:
return new OverzoomTileDataSource(new UrlTileDataSource(this, new TileDecoder(), getHttpEngine()), 14);

[devemux86]

Overzoom was created mainly for vector maps where rendering at large zoom can be done with content from upper levels.

Bitmap maps display images. Setting zoomMax in their builder, they show zoomed / blurry the tiles from upper zoom levels.

public static Builder<?> OPENSTREETMAP = BitmapTileSource.builder()
        .url("https://tile.openstreetmap.org")
        .zoomMax(14);

[demiantres]

Got it. This is exactly what I was looking for. Thank you.